This invention relates to a tubular or a rod-like ceramic article.
Ceramic materials are widely used in various industries. In particular, a large number of tubular or rod-like ceramic components having a precision shape, including a precision capillary tube having a minute bore are commercially produced as, for example, a fixing member, a guiding member, an aligning member, a reinforcing member, a coating member, a connecting member, or the like for an optical component or an electronic component. In the production of such precision components, it is a serious problem to accurately measure inside dimensions such as the size of the bores and to detect internal defects such as bubbles and cracks.
If the materials were transparent to a visible light, measurement of the inside dimensions and detection of the defects could easily be carried out by use of optical measuring instruments. However, since the ceramic material is opaque to the visible light in general, it is impossible to use the above mentioned approach.
Under the circumstances, various kinds of precision gauges are inevitably used for measurement of the dimensional accuracy. In this event, there arise problems that it takes a lot of time and labor and/or that it is impossible to measure an inner area to which no gauge is accessible. The detection of the internal defects is often carried out by a technique using an ultrasonic wave or a technique using a radioactive ray. However, each of these techniques is disadvantageous in that a measuring device is complicated and that test efficiency is low.
It is therefore an object of this invention to provide a tubular or a rod-like ceramic article which is opaque to the visible light and which is easy and efficient in measurement and inspection of its internal structure.
As a result of accumulation of diligent studies for the purpose of solving the above-described problems, the present inventors have found out that some of ceramic materials are transparent to an infrared ray although opaque to a visible light and that tubular articles or rod-like articles made of such infrared-transparent ceramic materials are easy in measurement and inspection of their internal structures by the use of the infrared ray, and hereby propose this invention.
A ceramic article according to this invention is a tubular or a rod-like ceramic article opaque to a visible light, and is characterized in that it is made of an infrared-transparent ceramic material having a transmittance not, in its thickness of 1 mm, less than 45%, preferably not less than 60%, for an infrared ray having a wavelength of 1550 nm and incident from the air.
In this invention, xe2x80x9copaque to the visible lightxe2x80x9d means that the measurement and the inspection of the internal structure by the use of the visible light are difficult and, more specifically, that the average transmittance for a direct-advancing light in the visible range (380-760 nm) is not greater than 50% when the thickness is equal to 1 mm.